U.S. patent number 7,557,063 [Application Number 11/898,807] was granted by the patent office on 2009-07-07 for noble metal-free nickel containing catalyst formulations for hydrogen generation.
This patent grant is currently assigned to Honda Giken Kogyo Kabushiki Kaisha, Symyx Technologies, Inc.. Invention is credited to Christopher James Brooks, Raymond E. Carhart, Alfred Hagemeyer, Michael Herrmann, Karin Yaccato.
United States Patent |
7,557,063 |
Hagemeyer , et al. |
July 7, 2009 |
Noble metal-free nickel containing catalyst formulations for
hydrogen generation
Abstract
The invention relates to noble metal-free nickel catalysts that
exhibit both high activity and selectivity to hydrogen generation
and carbon monoxide oxidation. The noble metal-free water gas shift
catalyst of the invention comprises Ni in either a supported or a
bulk state and at least one of Ge, Cd, In, Sn, Sb, Te, Pb, their
oxides and mixtures thereof.
Inventors: |
Hagemeyer; Alfred (Sunnyvale,
CA), Brooks; Christopher James (Dublin, OH), Carhart;
Raymond E. (Cupertino, CA), Yaccato; Karin (Santa Clara,
CA), Herrmann; Michael (Aglasterhausen-Michelbach,
DE) |
Assignee: |
Honda Giken Kogyo Kabushiki
Kaisha (Tokyo, JP)
Symyx Technologies, Inc. (Santa Clara, CA)
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Family
ID: |
32682077 |
Appl.
No.: |
11/898,807 |
Filed: |
September 17, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080051280 A1 |
Feb 28, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10739993 |
Dec 18, 2003 |
7270798 |
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60434631 |
Dec 20, 2002 |
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Current U.S.
Class: |
502/335; 502/60;
502/337; 502/332; 502/315; 502/310; 502/309; 502/308; 502/305;
423/437.2 |
Current CPC
Class: |
B01J
23/80 (20130101); B01J 23/825 (20130101); B01J
23/835 (20130101); C01B 3/16 (20130101); B01J
23/8435 (20130101); B01J 27/0576 (20130101); Y02E
60/32 (20130101); B01J 2219/00691 (20130101); B01J
2219/00747 (20130101); C01B 2203/1041 (20130101); B01J
2219/00612 (20130101); C40B 60/14 (20130101); C01B
2203/1052 (20130101); C40B 40/18 (20130101); B01J
2219/00641 (20130101); B01J 2219/00702 (20130101); C40B
30/08 (20130101); C01B 2203/00 (20130101); C01B
2203/1094 (20130101); B01J 2219/00637 (20130101); B01J
2219/00659 (20130101); Y02P 20/52 (20151101); B01J
2219/00364 (20130101); B01J 2219/00378 (20130101); B01J
2219/00745 (20130101); Y02E 60/324 (20130101); C01B
2203/0283 (20130101); C01B 2203/1082 (20130101); C01B
2203/1614 (20130101); C01B 2203/1088 (20130101); B01J
2219/00536 (20130101); B01J 2219/00605 (20130101) |
Current International
Class: |
B01J
23/755 (20060101); B01J 23/80 (20060101); B01J
23/825 (20060101); B01J 23/843 (20060101); C01B
31/20 (20060101) |
Field of
Search: |
;75/314,328
;502/335,325,328,337 ;423/437.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 189 701 |
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Aug 1986 |
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EP |
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0 149 799 |
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Oct 2001 |
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EP |
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Other References
NexTech Materials; Print-out of website
"http://www.nextechmaterials.com/products.htm"; Mar. 2001; 3 pages.
cited by other .
Xue, E., O'Keeffe, M., Ross, J.R.H.; Water-gas shift conversion
using a feed with a low steam to carbon monoxide ratio and
containing sulphur; Catalysis Today, 1996, vol. 30, pp. 107-118;
Elsevier Science B.V., The Netherlands. cited by other .
Hilaire, S., Wang, X., Luo, T., Gorte, R.J., Wagner, J.; A
comparative study of water-gas-shift reaction over ceria-supported
metallic catalysts; Applied Catalysis A: General, 2001, vol. 25,
pp. 271-278; Elsevier Science B.V., The Netherlands. cited by other
.
Rase, H.F., editor; Chapter 19--Synthesis Gas and Its Products;
Handbook of Commercial Catalysts--Heterogeneous Catalysts, 2000,
pp. 403-426;CRC Press, Boca Raton, Florida, US. cited by other
.
Li, Yue, Fu, Qi, Flytzani-Stephanopoulos, Maria; Low-temperature
water-gas shift reaction over Cu- and Ni-loaded cerium oxide
catalysts; Applied Catalysis B: Environmental, 2000, vol. 27; pp.
179-191; Elsevier Science B.V., The Netherlands. cited by
other.
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Primary Examiner: Langel; Wayne
Attorney, Agent or Firm: Capitol City TechLaw, PLLC Duell;
Mark E.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a divisional application of U.S. patent
application Ser. No. 10/739,993 filed Dec. 18, 2003, which claims
benefit from earlier filed U.S. Provisional Application No.
60/434,631, filed Dec. 20, 2002, which is incorporated herein in
its entirety by reference for all purposes. The present application
also incorporates by reference PCT International Patent Application
No. US2003/040386, entitled "Noble Metal-Free Nickel Catalyst
Formulations For Hydrogen Generation" naming as inventors Hagemeyer
et al. filed on the same day as the present application.
Claims
What we claim is:
1. A noble metal-free catalyst for catalyzing the water gas shift
reaction consisting essentially of: a) unsupported bulk Ni, b) In,
its oxides or mixtures thereof; and c) Cd, its oxides or mixtures
thereof.
2. The catalyst according to claim 1, wherein the water gas shift
catalyst comprises between about 0.05 wt. % to about 99 wt. %, with
respect to the total weight of all catalyst components, of Ni
present in the water gas shift catalyst.
3. The catalyst according to claim 1, wherein the water gas shift
catalyst comprises between about 0.50 wt. % to about 99 wt. %, with
respect to the total weight of all catalyst components, of Ni
present in the water gas shift catalyst.
4. A noble metal-free catalyst for catalyzing the water gas shift
reaction consisting essentially of: a) unsupported bulk Ni, b) Sn,
its oxides or mixtures thereof; and c) Cd, its oxides or mixtures
thereof.
5. The catalyst according to claim 4, wherein the water gas shift
catalyst comprises between about 0.05 wt. % to about 99 wt. %, with
respect to the total weight of all catalyst components, of Ni
present in the water gas shift catalyst.
6. The catalyst according to claim 4, wherein the water gas shift
catalyst comprises between about 0.50 wt. % to about 99 wt. %, with
respect to the total weight of all catalyst components, of Ni
present in the water gas shift catalyst.
7. A noble metal-free catalyst for catalyzing the water gas shift
reaction consisting essentially of: a) unsupported bulk Ni, b) In,
its oxides or mixtures thereof; and c) Sb, its oxides or mixtures
thereof.
8. The catalyst according to claim 7, wherein the water gas shift
catalyst comprises between about 0.05 wt. % to about 99 wt. %, with
respect to the total weight of all catalyst components, of Ni
present in the water gas shift catalyst.
9. The catalyst according to claim 7, wherein the water gas shift
catalyst comprises between about 0.50 wt. % to about 99 wt. %, with
respect to the total weight of all catalyst components, of Ni
present in the water gas shift catalyst.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and catalysts to generate a
hydrogen-rich gas from gas mixtures containing carbon monoxide and
water, such as water-containing syngas mixtures. More particularly,
the invention includes methods using noble metal-free nickel
catalysts where the nickel may exist in either a supported or a
bulk state. Catalysts of the invention exhibit both high activity
and selectivity to hydrogen generation and carbon monoxide
oxidation.
2. Discussion of the Related Art
Numerous chemical and energy-producing processes require a
hydrogen-rich composition (e.g. feed stream.) A hydrogen-rich feed
stream is typically combined with other reactants to carry out
various processes. Nitrogen fixation processes, for example,
produce ammonia by reacting feed streams containing hydrogen and
nitrogen under high pressures and temperatures in the presence of a
catalyst. In other processes, the hydrogen-rich feed stream should
not contain components detrimental to the process. Fuel cells such
as polymer electrode membrane ("PEM") fuel cells, produce energy
from a hydrogen-rich feed stream. PEM fuel cells typically operate
with a feed stream gas inlet temperature of less than 450.degree.
C. Carbon monoxide is excluded from the feed stream to the extent
possible to prevent poisoning of the electrode catalyst, which is
typically a platinum-containing catalyst. See U.S. Pat. No.
6,299,995.
One route for producing a hydrogen-rich gas is hydrocarbon steam
reforming. In a hydrocarbon steam reforming process steam is
reacted with a hydrocarbon fuel, such as methane, iso-octane,
toluene, etc., to produce hydrogen gas and carbon dioxide. The
reaction, shown below with methane (CH.sub.4), is strongly
endothermic; it requires a significant amount of heat.
CH.sub.4+2H.sub.2O.fwdarw.4H.sub.2+CO.sub.2 In the petrochemical
industry, hydrocarbon steam reforming of natural gas is typically
performed at temperatures in excess of 900.degree. C. Even for
catalyst assisted hydrocarbon steam reforming the temperature
requirement is often still above 700.degree. C. See, for example,
U.S. Pat. No. 6,303,098. Steam reforming of hydrocarbons, such as
methane, using nickel- and gold-containing catalysts and
temperatures greater than 450.degree. C. is described in U.S. Pat.
No. 5,997,835. The catalyzed process forms a hydrogen-rich gas,
with depressed carbon formation.
One example of effective hydrocarbon steam reforming catalysts is
the Sinfelt compositions which are composed of Pt, a Group 11
metal, and a Group 8-10 metal. Group 11 metals include Cu, Ag and
Au while Group 8-10 metals include the other noble metals. These
catalyst formulations are well known in the promotion of
hydrogenation, hydrogenolysis, hydrocracking, dealkylation of
aromatics, and naphtha reforming processes. See, for example, U.S.
Pat. Nos. 3,567,625 and 3,953,368. The application of catalysts
based on the Sinfelt model to the water gas shift ("WGS") reaction,
in particular at conditions suitable for lower temperature WGS
applications such as PEM fuel cells, has not been previously
reported.
Purified hydrogen-containing feed streams have also been produced
by filtering the gas mixture produced by hydrocarbon steam
reformation through hydrogen-permeable and hydrogen-selective
membranes. See, for example, U.S. Pat. No. 6,221,117. Such
approaches suffer from drawbacks due to the complexity of the
system and slow flow rates through the membranes.
Another method of producing a hydrogen-rich gas such as a feed
stream starts with a gas mixture containing hydrogen and carbon
monoxide with the absence of any substantial amount of water. For
instance, this may be the product of reforming a hydrocarbon or an
alcohol, and selectively removes the carbon monoxide from that gas
mixture. The carbon monoxide can be removed by absorption of the
carbon monoxide and/or by its oxidation to carbon dioxide. Such a
process utilizing a ruthenium based catalyst to remove and oxidize
the carbon monoxide is disclosed in U.S. Pat. No. 6,190,430.
The WGS reaction is another mechanism for producing a hydrogen-rich
gas but from water (steam) and carbon monoxide. An equilibrium
process, the water gas shift reaction, shown below, converts water
and carbon monoxide to hydrogen and carbon dioxide, and vice
versa.
##STR00001## Various catalysts have been developed to catalyze the
WGS reaction. These catalysts are typically intended for use at
temperatures greater than 450.degree. C. and/or pressures above 1
bar. For instance, U.S. Pat. No. 5,030,440 relates to a palladium
and platinum-containing catalyst formulation for catalyzing the
shift reaction at 550-650.degree. C. See also U.S. Pat. No.
5,830,425 for an iron/copper based catalyst formulation.
Catalytic conversion of water and carbon monoxide under water gas
shift reaction conditions has been used to produce hydrogen-rich
and carbon monoxide-poor gas mixtures. Existing WGS catalysts,
however, do not exhibit sufficient activity at a given temperature
to reach or even closely approach thermodynamic equilibrium
concentrations of hydrogen and carbon monoxide such that the
product gas may subsequently be used as a hydrogen feed stream.
Specifically, existing catalyst formulations are not sufficiently
active at low temperatures, that is, below about 450.degree. C. See
U.S. Pat. No. 5,030,440.
Platinum (Pt) is a well-known catalyst for both hydrocarbon steam
reforming and water gas shift reactions. Under typical hydrocarbon
steam reforming conditions, high temperature (above 850.degree. C.)
and high pressure (greater than 10 bar), the WGS reaction may occur
post-reforming over the hydrocarbon steam reforming catalyst due to
the high temperature and generally unselective catalyst
compositions. See, for instance, U.S. Pat. Nos. 6,254,807;
5,368,835; 5,134,109 and 5,030,440 for a variety of catalyst
compositions and reaction conditions under which the water gas
shift reaction may occur post-reforming.
Metals such as cobalt (Co), ruthenium (Ru), palladium (Pd), rhodium
(Rh) and nickel (Ni) have also been used as WGS catalysts but are
normally too active for the selective WGS reaction and cause
methanation of CO to CH.sub.4 under typical reaction conditions. In
other words, the hydrogen produced by the water gas shift reaction
is consumed as it reacts with the CO present in the presence of
such catalysts to yield methane. This methanation reaction activity
has limited the utility of metals such as Co, Ru, Pd, Rh and Ni as
water gas shift catalysts.
A need exists, therefore, for a efficient and economical method to
produce a hydrogen-rich syngas, and cost-effective catalysts which
are highly active and highly selective for both hydrogen generation
and carbon monoxide oxidation at moderate temperatures (e.g. below
about 450.degree. C.) to provide a hydrogen-rich syngas from a gas
mixture containing hydrogen and carbon monoxide.
SUMMARY OF THE INVENTION
The invention meets the need for highly active, selective and
economical catalysts for the generation of hydrogen and the
oxidation of carbon monoxide and to thereby provide a hydrogen-rich
gas, such as a hydrogen-rich syngas, from a gas mixture of at least
carbon monoxide and water. Accordingly, the invention provides
methods and catalysts for producing a hydrogen-rich gas.
The invention is, in a first general embodiment, a method for
producing a hydrogen-rich gas (e.g., syngas) by contacting a
CO-containing gas, such as a syngas mixture, with a noble
metal-free nickel-containing water gas shift catalyst in the
presence of water at a temperature of not more than about
450.degree. C. In a second general embodiment, the noble metal-free
water gas shift catalyst comprises Ni in either a supported or a
bulk state and at least one of Ge, Cd, In, Sn, Sb, Te, Pb, their
oxides and mixtures thereof. Carriers for the supported catalysts
may be, for example, at least one member selected from the group
consisting of alumina, zirconia, titania, ceria, magnesia,
lanthania, niobia, yttria, iron oxide and mixtures thereof. The
method of the invention may be conducted at a temperature ranging
from about 150.degree. C. to about 450.degree. C.
In third general embodiment, the invention is directed to the
aforementioned noble metal-free nickel-containing water gas shift
catalysts in an apparatus for generating a hydrogen gas containing
stream from a hydrocarbon or substituted hydrocarbon feed stream.
The apparatus further comprises, in addition to the WGS catalyst, a
fuel reformer, a water gas shift reactor and a temperature
controller.
The following described preferred embodiments of the WGS catalyst
can be used in each one of the three general embodiments or in
specific, related embodiments (e.g., fuel cell reactors, fuel
processors and hydrocarbon steam reformers.)
In one preferred embodiment, the water gas shift catalyst comprises
Ni and at least one of Ge, Cd, In, Sn, Sb, Te, Pb, their oxides and
mixtures thereof
In a second preferred embodiment, the water gas shift catalyst
comprises Ni in a bulk state and at least one of Ge, Cd, Sb, Te,
Pb, their oxides and mixtures thereof.
In a third preferred embodiment, the water gas shift catalyst
comprises Ni in a bulk state; In, its oxides or mixtures thereof;
and Cd, its oxides or mixtures thereof.
In another preferred embodiment, the water gas shift catalyst
comprises Ni in a bulk state; In, its oxides or mixtures thereof;
and Sb, its oxides or mixtures thereof.
In another preferred embodiment, the water gas shift catalyst
comprises Ni in a bulk state; Sn, its oxides or mixtures thereof;
and Cd, its oxides or mixtures thereof.
In yet another preferred embodiment, the water gas shift catalyst
comprises Ni in a bulk state; Sn, its oxides or mixtures thereof;
and Sb, its oxides or mixtures thereof.
In yet another preferred embodiment, the water gas shift catalyst
comprises Ni in a bulk state; Sn, its oxides or mixtures thereof;
and Te, its oxides or mixtures thereof.
In yet another preferred embodiment, the water gas shift catalyst
comprises supported Ni and at least one of In, Sn, Te, their oxides
and mixtures thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
The accompanying drawings, which are included to provide a further
understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate preferred
embodiments of the invention and together with the detailed
description serve to explain the principles of the invention. In
the drawings:
FIGS. 1A and 1B illustrate the process of producing a library test
wafer, and
FIGS. 1C and 1D illustrate SpotFire plots of the CO and H.sub.2O
conversion versus CO.sub.2 production for the wafer under WGS
conditions at various temperatures. The legend for FIG. 1A also
applies to FIG. 1B exclusively.
FIG. 2 illustrates plots of CO concentration versus temperature for
scaled-up catalyst samples under WGS conditions.
FIGS. 3A-3F illustrate the compositional make-up of various
exemplary library test wafers. The legend for FIGS. 3A-3C applies
only to FIGS. 3A-3C. The legend for FIGS. 3D-3F applies only to
FIGS. 3D-3F.
FIG. 4A illustrates a representative plot of CO conversion versus
CO2 production for a prototypical library test wafer at various
temperatures,
FIG. 4B illustrates the effect of catalyst selectivity and activity
versus the WGS mass balance, and
FIG. 4C illustrates the effect of temperature on catalyst
performance under WGS conditions.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to a method for producing a hydrogen-rich
gas, such as a hydrogen-rich syngas. According to the method, a
CO-containing gas, such as a CO-containing syngas, contacts a noble
metal-free nickel-containing water gas shift catalyst, in the
presence of water, preferably a stoichiometric excess of water,
preferably at a reaction temperature of less than about 450.degree.
C. to produce a hydrogen-rich gas, such as a hydrogen-rich syngas.
The reaction pressure is preferably not more than about 10 bar. The
invention also relates to a noble metal-free nickel-containing
water gas shift catalyst itself and to apparatus such as a water
gas shift reactors and fuel processing apparatus comprising such
WGS catalysts.
A water gas shift catalyst according to the invention comprises: a)
Ni and b) at least one of Ge, Cd, In, Sn, Sb, Te, Pb, their oxides
and mixtures thereof. The WGS catalyst may be supported on a
carrier, such as any one member or a combination of alumina,
zirconia, titania, ceria, magnesia, lanthania, niobia, zeolite,
perovskite, silica clay, yttria and iron oxide.
The WGS catalysts of the invention comprise combinations of at
least two metals or metalloids, selected from Ni and the group as
indicated above, in each and every possible permutation and
combination, except as specifically and expressly excluded.
Although particular subgroupings of preferred combinations of
metals or metalloids are also presented, the present invention is
not limited to the particularly recited subgroupings.
Discussion regarding the particular function of various components
of catalysts and catalyst systems is provided herein solely to
explain the advantage of the invention, and is not limiting as to
the scope of the invention or the intended use, function, or
mechanism of the various components and/or compositions disclosed
and claimed. As such, any discussion of component and/or
compositional function is made, without being bound by theory and
by current understanding, unless and except such requirements are
expressly recited in the claims. Generally, for example, and
without being bound by theory, Ni promotes the unwanted methanation
reaction. The metals or metalloids of component b) may themselves
have activity as WGS catalysts but function in combination with Ni
to attenuate the methanation reaction and to impart beneficial
properties to the catalyst of the invention.
Catalysts of the invention can catalyze the WGS reaction at varying
temperatures, avoid or attenuate unwanted side reactions such as
methanation reactions, as well as generate a hydrogen-rich gas,
such as a hydrogen-rich syngas. The composition of the WGS
catalysts of the invention and their use in WGS reactions are
discussed below.
1. Definitions
Water gas shift ("WGS") reaction: Reaction which produces hydrogen
and carbon dioxide from water and carbon monoxide, and vice
versa:
##STR00002##
Generally, and unless explicitly stated to the contrary, each of
the WGS catalysts of the invention can be advantageously applied
both in connection with the forward reaction as shown above (i.e.,
for the production of H.sub.2), or alternatively, in connection
with the reverse reaction as shown above (i.e., for the production
of CO). As such, the various catalysts disclosed herein can be used
to specifically control the ratio of H.sub.2 to CO in a gas
stream.
Methanation reaction: Reaction which produces methane and water
from a carbon source, such as carbon monoxide or carbon dioxide,
and hydrogen: CO+3H.sub.2.fwdarw.CH.sub.4+H.sub.2O
CO.sub.2+4H.sub.2.fwdarw.CH.sub.4+2H.sub.2O
"Syngas " (also called synthesis gas): Gaseous mixture comprising
hydrogen (H.sub.2) and carbon monoxide (CO) which may also contain
other gas components such as carbon dioxide (CO.sub.2), water
(H.sub.2O), methane (CH.sub.4) and nitrogen (N.sub.2).
LTS: Refers to "low temperature shift" reaction conditions where
the reaction temperature is less than about 250.degree. C.,
preferably ranging from about 150.degree. C. to about 250.degree.
C.
MTS: Refers to "medium temperature shift" reaction conditions where
the reaction temperature ranges from about 250.degree. C. to about
350.degree. C.
HTS: Refers to "high temperature shift" reaction conditions where
the reaction temperature is more than about 350.degree. C. and up
to about 450.degree. C.
Hydrocarbon: Compound containing hydrogen, carbon, and, optionally,
oxygen.
The Periodic Table of the Elements is based on the present IUPAC
convention, thus, for example, Group 11 comprises Cu, Ag and Au.
(See http://www.iupac.org dated May 30, 2002.)
As discussed herein, the catalyst composition nomenclature uses a
dash (i.e., "--") to separate catalyst component groups where a
catalyst may contain one or more of the catalyst components listed
for each component group, brackets (i.e., "{ }") are used to
enclose the members of a catalyst component group, "{two of . . .
}" is used if two or more members of a catalyst component group are
required to be present in a catalyst composition, "blank" is used
within the "{ }" to indicate the possible choice that no additional
element is added, and a slash (i.e., "/") is used to separate
supported catalyst components from their support material, if any.
Additionally, the elements within a catalyst composition
formulation include all possible oxidation states, including
oxides, or salts, or mixtures thereof.
Using this shorthand nomenclature in this specification, for
example, "Pt--{Rh, Ni}-{Na, K, Fe, Os}/ZrO.sub.2" would represent
catalyst compositions containing Pt, one or more of Rh and Ni, and
one or more of Na, K, Fe, and Os supported on ZrO.sub.2; all of the
catalyst elements may be in any possible oxidation state, unless
explicitly indicated otherwise. "Pt--Rh--Ni-{two of Na, K, Fe, Os}"
would represent a supported or unsupported catalyst composition
containing Pt, Rh, and Ni, and two or more of Na, K, Fe, and Os.
"Rh--{Cu,Ag,Au}--{Na, K, blank}/TiO.sub.2" would represent catalyst
compositions containing Rh, one or more of Cu, Ag and Au, and,
optionally, and one of Na or K supported on TiO.sub.2.
The description of a catalyst composition formulation as having an
essential absence of an element, or being "element-free" or
"substantially element free" does allow for the presence of an
insignificant, non-functional amount of the specified element to be
present, for example, as a non-functional impurity in a catalyst
composition formulation. However, such a description excludes
formulations where the specific element has been intentionally or
purposefully added to the formulation to achieve a certain
measurable benefit. Typically, with respect to noble metals such as
Pt for example, amounts less than about 0.01 weight percentage
would not usually impart a material functional benefit with respect
to catalyst performance, and therefore such amounts would generally
be considered as an insignificant amount, or not more than a mere
impurity. In some embodiments, however, amounts up to less than
about 0.04 weight percent may be included without a material
functional benefit to catalyst performance. In other embodiments,
amounts less than about 0.005 weight percent would be considered an
insignificant amount, and therefore a non-functional impurity.
2. WGS Catalyst
A noble metal-free nickel containing water gas shift catalyst of
the invention comprises: a) Ni and b) at least one of Ge, Cd, In,
Sn, Sb, Te, Pb, their oxides and mixtures thereof. The catalyst
components are typically present in a mixture of the reduced or
oxide forms; typically one of the forms will predominate in the
mixture. The nickel may be in a supported state or in an
unsupported bulk state. Suitable carriers for supported catalysts
are discussed below.
The catalyst components are typically present in a mixture of the
reduced or oxide forms; typically, one of the forms will
predominate in the mixture. A WGS catalyst of the invention may be
prepared by mixing the metals and/or metalloids in their elemental
forms or as oxides or salts to form a catalyst precursor. This
catalyst precursor mixture generally undergoes a calcination and/or
reductive treatment, which may be in-situ (within the reactor),
prior to use as a WGS catalyst. Without being bound by theory, the
catalytically active species are generally understood to be species
which are in the reduced elemental state or in other possible
higher oxidation states. The catalyst precursor species are
believed to be substantially completely converted to the
catalytically active species by the pre-use treatment. Nonetheless,
the catalyst component species present after calcination and/or
reduction may be a mixture of catalytically active species such as
the reduced metal or other possible higher oxidation states and
uncalcined or unreduced species depending on the efficiency of the
calcination and/or reduction conditions.
A. Catalyst Compositions
As discussed above, one embodiment of the invention is a noble
metal-free nickel-containing catalyst for catalyzing the water gas
shift reaction (or its reverse reaction). According to the
invention, a WGS catalyst may have the following composition: a) Ni
and b) at least one of Ge, Cd, In, Sn, Sb, Te, Pb, their oxides and
mixtures thereof.
The amount of each component present in a given catalyst according
to the present invention may vary depending on the reaction
conditions under which the catalyst is intended to operate.
Generally, the nickel component may be present in an amount ranging
from about 0.05 wt. % to about 99 wt. %, preferably about 0.10 wt.
% to about 99 wt. %, and more preferably about 0.50 wt. % to about
99 wt. %.
Component b) may be present in an amount ranging from about 5 wt. %
to about 50 wt. %.
The above weight percentages are calculated based on the total
weight of the catalyst component in its final state in the catalyst
composition after the final catalyst preparation step (i.e., the
resulting oxidation state or states) with respect to the total
weight of all catalyst components plus the support material, if
any. The presence of a given catalyst component in the support
material and the extent and type of its interaction with other
catalyst components may effect the amount of a component needed to
achieve the desired performance effect.
Other WGS catalysts which embody the invention are listed below.
Utilizing the shorthand notation discussed above, where each metal
may be present in its reduced form or in a higher oxidation state.
The following compositions are examples of preferred catalyst
compositions: bulk Ni--{Ge, Cd, Sb, Te, Pb}; bulk Ni--In--Cd; bulk
Ni--In--Sb; bulk Ni--Sn--Cd; bulk Ni--Sn--Sb; bulk Ni--Sn--Te; and
supported Ni--{In, Sn, Te}.
Some catalysts may be more advantageously applied in specific
operating temperature ranges. For instance, some Ni containing
catalysts are generally more active and selective under HTS
conditions than at lower temperature ranges. Specifically, for
example, a Ni-containing catalyst, including especially noble
metal-free Ni-containing catalyst and at least one of component
chosen from among the following: Ge, Cd, In, Sn, Sb, Te or Pb is
preferred at HTS conditions.
B. Catalyst Component a): Ni
A first component in a catalyst of the invention is Ni, component
a). Unmodified Ni has been shown to catalyze the methanation
reaction under WGS conditions. However, according to the present
invention, Ni may be converted to a highly active and selective WGS
catalyst by adjusting the Ni loading and by combining with other
catalyst components which may moderate the activity of the
methanation reaction. According to the present invention, various
non-noble metal dopants (e.g. Ge, Cd, In, Sn, Sb, Te and Pb) may be
added to Ni to generate catalysts that are highly active and
selective WGS catalysts, and exhibit increased selectivity for the
WGS reaction over the competing methanation reaction.
Preferably, the Ni has to be reduced to the active metallic state
prior to use, typically by a reduction pretreatment in H.sub.2 at
about 350.degree. C. to about 400.degree. C. because nickel oxide
requires temperatures above about 300.degree. C. for reduction to
occur. Metallic nickel particles tend to sinter irreversibly at
temperatures in excess of about 400.degree. C. Mn and Cr are
examples of dopants that stabilize Ni against sintering.
The Ni used in the catalysts of the invention may be dispersed
through mixing with an inert binder/carrier/dispersant which
decreases the overall achievable Ni loading. Alternatively, the Ni
used in the catalysts may exist in an unsupported bulk state which
reflects high Ni loading.
C. Catalyst Components b): "Functional" Metals or Metalloids
The WGS catalysts of the invention contain at least two metals or
metalloids. In addition to the Ni as component a), discussed above,
a WGS catalyst contains metals or metalloids which, when used in
combination with Ni, function to impart beneficial properties to
the catalyst of the invention. A catalyst of the invention, then,
further comprises at least one of Ge, Cd, In, Sn, Sb, Te, Pb, their
oxides and mixtures thereof as component b).
To minimize its methanizing properties, Ni may be combined with,
for example, Group I, Group II and main group metals to form
suitable WGS catalysts. In, Sn and Te are preferred dopants for
supported Ni (i.e. low Ni loading) catalysts, whereas Cd, Pb and Ge
are preferred dopants for bulk Ni (i.e. high Ni loading)
catalysts.
Examples of carriers for the supported Ni catalysts include, for
instance, alumina, zirconia, titania, ceria, magnesia, lanthania,
niobia, yttria, zeolite, perovskite, silica clay, cobalt oxide,
iron oxide and mixtures thereof. Preferred carriers include cobalt
oxide, zirconia and titania. Perovskite may also be utilized as a
support for the inventive catalyst formulations. A preferred
supported catalyst is, for example, Ni--Sn--Te/ZrO.sub.2.
D. Functional Classification of Catalyst Components
Without limiting the scope of the invention, discussion of the
functions of the various catalyst components is offered, along with
a template for composing catalyst compositions according to the
invention. The following classification of catalyst components will
direct one of skill in the art in the selection of various catalyst
components to formulate WGS catalyst compositions according to the
present invention and depending on the reaction conditions of
interest.
Furthermore, according to the invention, there are several classes
of catalyst components and metals which may be incorporated into a
water gas shift catalyst. Hence, the various elements recited as
components in any of the described embodiments (e.g., as component
(b)), may be included in any various combination and permutation to
achieve a catalyst composition that is coarsely or finely tuned for
a specific application (e.g. including for a specific set of
conditions, such as, temperature, pressure, space velocity,
catalyst precursor, catalyst loading, catalyst surface
area/presentation, reactant flow rates, reactant ratios, etc.). In
some cases, the effect of a given component may vary with the
operating temperature for the catalyst. These catalyst components
may function as, for instance, activators or moderators depending
upon their effect on the performance characteristics of the
catalyst. For example, if greater activity is desired, an activator
may be incorporated into a catalyst, or a moderator may be replaced
by at least one activator or, alternatively, by at least one
moderator one step further up the "activity ladder." An "activity
ladder" ranks secondary or added catalyst components, such as
activators or moderators, in order of the magnitude of their
respective effect on the performance of a principal catalyst
constituent. Conversely, if WGS selectivity of a catalyst needs to
be increased (e.g., decrease the occurrence of the competing
methanation reaction), then either an activator may be removed from
the catalyst or, alternatively, the current moderator may be
replaced by at least one moderator one step down the "activity
ladder." The function of these catalyst component may be further
described as "hard" or "soft" depending on the relative effect
obtained by incorporating a given component into a catalyst. The
catalyst components may be metals, metalloids, or non-metals. For
the catalysts of the invention, for example, In, Sn and Te are soft
moderators that are preferred for supported Ni systems whereas hard
(i.e. more deactivating) moderators such as Ge, Cd and Pb are
preferred for the bulk Ni systems.
Typically, a WGS catalyst suitable for use under LTS conditions
employs, for example, activators and may only be minimally
moderated, if at all, because activation is generally the important
parameter to be considered under LTS conditions. Such LTS catalysts
also may preferably employ high surface area carriers to enhance
catalyst activity. Conversely, WGS catalysts used in HTS conditions
may benefit from the catalyst being moderated because selectivity
and methanation are parameters to be considered. Such HTS catalysts
may use, for example, low surface area carriers. Accordingly,
operating temperature may be considered in selecting a WGS catalyst
according to the present invention for a particular operating
environment.
Moderators may also include Ge, Cd, In, Sn, Sb and Te. Typically,
for moderators to exert a moderating function on Ni, they should be
substantially in the reduced or metallic state. Ge alloyed with Sn
is an example of an alloy that was found to be highly active, even
for low temperature systems, when in the fully oxidized state, that
is, when treated at a pre-reduction temperature of about
300.degree. C. which reduces the noble metals (such as Pt, Rh, or
Pd) selectively but does not change the active oxidized state of
the redox dopants in a catalyst composition.
E. Supports
The support or carrier may be any support or carrier used with the
catalyst which allows the water gas shift reaction to proceed. The
support or carrier may be a porous, adsorptive, high surface area
support with a surface area of about 25 to about 500 m.sup.2/g. The
porous carrier material may be relatively inert to the conditions
utilized in the WGS process, and may include carrier materials that
have traditionally be utilized in hydrocarbon steam reforming
processes, such as, (1) activated carbon, coke, or charcoal; (2)
silica or silica gel, silicon carbide, clays, and silicates
including those synthetically prepared and naturally occurring, for
example, china clay, diatomaceous earth, fuller's earth, kaolin,
etc.; (3) ceramics, porcelain, bauxite; (4) refractory inorganic
oxides such as alumina, titanium dioxide, zirconium oxide,
magnesia, etc.; (5) crystalline and amorphous aluminosilicates such
as naturally occurring or synthetically prepared mordenite and/or
faujasite; and, (6) combinations of these groups.
When a WGS catalyst of the invention is a supported catalyst, the
support utilized may contain one or more of the metals (or
metalloids) of the catalyst. The support may contain sufficient or
excess amounts of the metal for the catalyst such that the catalyst
may be formed by combining the other components with the support.
Examples of such supports include ceria which can contribute
cerium, Ce, to a catalyst, or iron oxide which can contribute iron,
Fe. When such supports are used the amount of the catalyst
component in the support typically may be far in excess of the
amount of the catalyst component needed for the catalyst. Thus the
support may act as both an active catalyst component and a support
material for the catalyst. Alternatively, the support may have only
minor amounts of a metal making up the WGS catalyst such that the
catalyst may be formed by combining all desired components on the
support.
Carrier screening with catalysts containing Pt as the only active
noble metal revealed that a water gas shift catalyst may also be
supported on a carrier comprising alumina, zirconia, titania,
ceria, magnesia, lanthania, niobia, yttria and iron oxide.
Perovskite (ABO.sub.3) may also be utilized as a support for the
inventive catalyst formulations.
Zirconia, titania and ceria may be supports for the present
invention and provide high activity for the WGS reaction.
Preferably, zirconia is in the monoclinic phase. Niobia, yttria and
iron oxide carriers provide high selectivity but are also less
active which is believed to be due to a lack of surface area. Pt on
magnesia carriers formulated to have high surface areas
(approximately 100 m.sup.2/g) exhibit high selectivity but also
exhibit activity which decreases rapidly with falling reaction
temperature.
Iron, yttrium, and magnesium oxides may be utilized as primary
layers on zirconia carriers to provide both higher surface area and
low moderator concentration.
In general, alumina has been found to be an active but unselective
carrier for Pt only containing WGS catalysts. However, the
selectivity of gamma alumina may be improved by doping with Zr
and/or Co or one of the rare earth elements, such as, for example,
La and Ce. This doping may be accomplished by addition of the
oxides or other salts such as nitrates, in either liquid or solid
form, to the alumina. Other possible dopants to increase the
selectivity include redox dopants, such as for instance, Re, Mo, Fe
and basic dopants. Preferred is an embodiment of gamma alumina
combined with Zr and/or Co which exhibits both high activity and
selectivity over a broad temperature range.
High surface area aluminas, such as gamma-, delta- or theta-alumina
are preferred alumina carriers. Other alumina carriers, such as
mixed silica alumina, sol-gel alumina, as well as sol-gel or
co-precipitated alumina-zirconia carriers may be used. Alumina
typically has a higher surface area and a higher pore volume than
carriers such as zirconia and offers a price advantage over other
more expensive carriers.
F. Methods of Making a WGS Catalyst
As set forth above, a WGS catalyst of the invention may be prepared
by mixing the metals and/or metalloids in their elemental forms or
as oxides or salts to form a catalyst precursor, which generally
undergoes a calcination and/or reductive treatment. Without being
bound by theory, the catalytically active species are generally
understood to be species which are in the reduced elemental state
or in other possible higher oxidation states.
The WGS catalysts of the invention may be prepared by any well
known catalyst synthesis processes. See, for example, U.S. Pat.
Nos. 6,299,995 and 6,293,979. Spray drying, precipitation,
impregnation, incipient wetness, ion exchange, fluid bed coating,
physical or chemical vapor deposition are just examples of several
methods that may be utilized to make the present WGS catalysts.
Preferred approaches, include, for instance, impregnation or
incipient wetness. The catalyst may be in any suitable form, such
as, pellets, granular, bed, or monolith. See also co-pending U.S.
patent application Ser. No. 10/739,428, entitled "Methods For The
Preparation of Catalysts For Hydrogen Generation" to Hagemeyer et
al., filed on the same date as the present application, for further
details on methods of catalyst preparation and catalyst precursors.
The complete disclosure of the above mentioned application and all
other references cited herein are incorporated herein in their
entireties for all purposes.
The WGS catalyst of the invention may be prepared on a solid
support or carrier material. Preferably, the support or carrier is,
or is coated with, a high surface area material onto which the
precursors of the catalyst are added by any of several different
possible techniques, as set forth above and as known in the art.
The catalyst of the invention may be employed in the form of
pellets, or on a support, preferably a monolith, for instance a
honeycomb monolith.
Catalyst precursor solutions are preferably composed of easily
decomposable forms of the catalyst component in a sufficiently high
enough concentration to permit convenient preparation. Examples of
easily decomposable precursor forms include the nitrate, amine, and
oxalate salts. Typically chlorine containing precursors are avoided
to prevent chlorine poisoning of the catalyst. Solutions can be
aqueous or non-aqueous solutions. Exemplary non-aqueous solvents
can include polar solvents, aprotic solvents, alcohols, and crown
ethers, for example, tetrahydrofuran and ethanol. Concentration of
the precursor solutions generally may be up to the solubility
limitations of the preparation technique with consideration given
to such parameters as, for example, porosity of the support, number
of impregnation steps, pH of the precursor solutions, and so forth.
The appropriate catalyst component precursor concentration can be
readily determined by one of ordinary skill in the art of catalyst
preparation.
Ni--Nickel nitrate, Ni(NO.sub.3).sub.2, and nickel formate are both
possible nickel precursors. The nickel formate may be prepared by
dissolving Ni(HCO.sub.2).sub.2 in water and adding formic acid, or
by dissolving in dilute formic acid, to produce clear greenish
solutions. Nickel acetate, Ni(OAc).sub.2, may be used as nickel
precursor. NiSO.sub.4 may also be used as a catalyst precursor.
Nickel chloride, NiCl.sub.2, may be used when precipitating Ni
hydroxide or Ni carbonate. Catalyst poisoning due to residual
chloride is not an issue for base metal catalysts such as bulk
nickel as it is for noble metals. A bulk Ni catalyst (grade: 0104P)
is commercially available from suppliers such as Engelhard.
Ge--Germanium oxalate may be prepared from amorphous Ge(IV) oxide,
glycol-soluble GeO.sub.2, (Aldrich) by reaction with 1M aqueous
oxalic acid at room temperature. H.sub.2GeO.sub.3 may be prepared
by dissolving GeO.sub.2 in water at 80.degree. C. and adding 3
drops of NH.sub.4OH (25%) to produce a clear, colorless
H.sub.2GeO.sub.3 solution. (NMe.sub.4).sub.2GeO.sub.3 may be
prepared by dissolving 0.25M GeO.sub.2 in 0.1 M NMe.sub.4OH.
(NH.sub.4).sub.2GeO.sub.3 may be prepared by dissolving 0.25 M
GeO.sub.2 in 0.25M NH.sub.4OH.
Cd--Cadmium nitrate is water soluble and a suitable catalyst
precursor.
In--Indium formate and indium nitrate are preferred precursors for
indium.
Sn--Tin oxalate produced by reacting the acetate with oxalic acid
may be used as a catalyst precursor. Tin tartrate,
SnC.sub.4H.sub.4O.sub.6, in NMe.sub.4OH at about 0.25M Sn
concentration, and tin actetate, also dissolved in NMe.sub.4OH at
about 0.25M Sn concentration, may be used as catalyst
precursors.
Sb--Ammonium antimony oxalate produced by reacting the acetate with
oxalic acid and ammonia is a suitable antimony precursor. Antimony
oxalate, Sb.sub.2(C.sub.2O.sub.4).sub.3, available from Pfaltz
& Bauer, is a water soluble precursor. Potassium antimony
oxide, KSbO.sub.3, and antimony citrate, prepared by stirring
antimony(II) acetate in 1 M citric acid at room temperature, are
both possible catalyst precursors.
Te--Telluric acid, Te(OH).sub.6, may be used as a precursor for
tellurium.
Pb--Lead nitrate is a possible lead precursor.
3. Producing a Hydrogen-Rich Gas, Such as, a Hydrogen-Rich
Syngas
The invention also relates to a method for producing a
hydrogen-rich gas, such as a hydrogen-rich syngas. An additional
embodiment of the invention may be directed to a method of
producing a CO-depleted syngas.
A CO-containing gas, such as a syngas, contacts a water gas shift
catalyst in the presence of water according to the method of the
invention. The reaction preferably may occur at a temperature of
less than 450.degree. C. to produce a hydrogen-rich gas, such as a
hydrogen-rich syngas.
A method of the invention may be utilized over a broad range of
reaction conditions. Preferably, the method is conducted at a
pressure of no more than about 75 bar, preferably at a pressure of
no more than about 50 bar to produce a hydrogen-rich syngas. Even
more preferred is to have the reaction occur at a pressure of no
more than about 25 bar, or even no more than about 15 bar, or not
more than about 10 bar. Especially preferred is to have the
reaction occur at, or about atmospheric pressure. Depending on the
formulation of the catalyst according to the present invention, the
present method may be conducted at reactant gas temperatures
ranging from less than about 250.degree. C. to up to about
450.degree. C. Preferably, the reaction occurs at a temperature
selected from one or more temperature subranges of LTS, MTS and/or
HTS as described above. Space velocities may range from about 1
hr.sup.-1 up to about 1,000,000 hr.sup.-1. Feed ratios,
temperature, pressure and the desired product ratio are factors
that would normally be considered by one of skill in the to
determined a desired space velocity for a particular catalyst
formulation.
4. Fuel Processor Apparatus
The invention further relates to a fuel processing system for
generation of a hydrogen-rich gas from a hydrocarbon or substituted
hydrocarbon fuel. Such a fuel processing system would comprise, for
example, a fuel reformer, a water gas shift reactor and a
temperature controller.
The fuel reformer would convert a fuel reactant stream comprising a
hydrocarbon or a substituted hydrocarbon fuel to a reformed product
stream comprising carbon monoxide and water. The fuel reformer may
typically have an inlet for receiving the reactant stream, a
reaction chamber for converting the reactant stream to the product
stream and an outlet for discharging the product stream.
The fuel processor would also comprise a water gas shift reactor
for effecting a water gas shift reaction at a temperature of less
than about 450.degree. C. This water gas shift reactor may comprise
an inlet for receiving a water gas shift feed stream comprising
carbon monoxide and water from the product stream of the fuel
reformer, a reaction chamber having a water gas shift catalyst as
described herein located therein and an outlet for discharging the
resulting hydrogen-rich gas. The water gas shift catalyst would
preferably be effective for generating hydrogen and carbon dioxide
from the water gas shift feed stream.
The temperature controller may be adapted to maintain the
temperature of the reaction chamber of the water gas shift reactor
at a temperature of less than about 450.degree. C.
5. Industrial Applications
Syngas is used as a reactant feed in number of industrial
applications, including for example, methanol synthesis, ammonia
synthesis, oxoaldehyde synthesis from olefins (typically in
combination with a subsequent hydrogenation to form the
corresponding oxoalcohol), hydrogenations and carbonylations. Each
of these various industrial applications preferably includes a
certain ratio of H.sub.2 to CO in the syngas reactant stream. For
methanol synthesis the ratio of H.sub.2:CO is preferably about 2:1.
For oxosynthesis of oxoaldehydes from olefins, the ratio of
H.sub.2:CO is preferably about 1:1. For ammonia synthesis, the
ratio of H.sub.2 to N.sub.2 (e.g., supplied from air) is preferably
about 3:1. For hydrogenations, syngas feed streams that have higher
ratios of H.sub.2:CO are preferred (e.g., feed streams that are
H.sub.2 enriched, and that are preferably substantially H.sub.2
pure feed streams). Carbonylation reactions are preferably effected
using feed streams that have lower ratios of H.sub.2:CO (e.g., feed
streams that are CO enriched, and that are preferably substantially
CO pure feed streams).
The WGS catalysts of the present invention, and the methods
disclosed herein that employ such WGS catalysts, can be applied
industrially to adjust or control the relative ratio H.sub.2:CO in
a feed stream for a synthesis reaction, such as methanol synthesis,
ammonia synthesis, oxoaldehyde synthesis, hydrogenation reactions
and carbonylation reactions. In one embodiment, for example, a
syngas product stream comprising CO and H.sub.2 can be produced
from a hydrocarbon by a reforming reaction in a reformer (e.g., by
steam reforming of a hydrocarbon such as methanol or naphtha). The
syngas product stream can then be fed (directly or indirectly after
further downstream processing) as the feed stream to a WGS reactor,
preferably having a temperature controller adapted to maintain the
temperature of the WGS reactor at a temperature of about
450.degree. C. or less during the WGS reaction (or at lower
temperatures or temperature ranges as described herein in
connection with the catalysts of the present invention). The WGS
catalyst(s) employed in the WGS reactor are preferably selected
from one or more of the catalysts and/or methods of the invention.
The feed stream to the WGS reactor is contacted with the WGS
catalyst(s) under reaction conditions effective for controlling the
ratio of H.sub.2:CO in the product stream from the WGS reactor
(i.e., the "shifted product stream") to the desired ratio for the
downstream reaction of interest (e.g., methanol synthesis),
including to ratios described above in connection with the various
reactions of industrial significance. As a non-limiting example, a
syngas product stream from a methane steam reformer will typically
have a H.sub.2:CO ratio of about 6:1. The WGS catalyst(s) of the
present invention can be employed in a WGS reaction (in the forward
direction as shown above) to further enhance the amount of H.sub.2
relative to CO, for example to more than about 10:1, for a
downstream hydrogenation reaction. As another example, the ratio of
H.sub.2:CO in such a syngas product stream can be reduced by using
a WGS catalyst(s) of the present invention in a WGS reaction (in
the reverse direction as shown above) to achieve or approach the
desired 2:1 ratio for methanol synthesis. Other examples will be
known to a person of skill in the art in view of the teachings of
the present invention.
A person of skill in the art will understand and appreciate that
with respect to each of the preferred catalyst embodiments as
described in the preceding paragraphs, the particular components of
each embodiment can be present in their elemental state or in one
or more oxide states or mixtures thereof.
Although the foregoing description is directed to the preferred
embodiments of the invention, it is noted that other variations and
modifications will be apparent to those skilled in the art, and
which may be made without departing from the spirit or scope of the
invention.
EXAMPLES
General
Small quantity catalyst composition samples are generally prepared
by automated liquid dispensing robots (Cavro Scientific
Instruments) on flat quartz test wafers.
Generally, supported catalysts are prepared by providing a catalyst
support (e.g. alumina, silica, titania, etc.) to the wafer
substrate, typically as a slurry composition using a
liquid-handling robot to individual regions or locations on the
substrate or by wash-coating a surface of the substrate using
techniques known to those of skill in the art, and drying to form
dried solid support material on the substrate. Discrete regions of
the support-containing substrate are then impregnated with
specified compositions intended to operate as catalysts or catalyst
precursors, with the compositions comprising metals (e.g. various
combinations of transition metal salts). In some circumstances the
compositions are delivered to the region as a mixture of different
metal-containing components and in some circumstances (additionally
or alternatively) repeated or repetitive impregnation steps are
performed using different metal-containing precursors. The
compositions are dried to form supported catalyst precursors. The
supported catalyst precursors are treated by calcining and/or
reducing to form active supported catalytic materials at discrete
regions on the wafer substrate.
Bulk catalysts (e.g. noble-metal-free Ni-containing catalysts) may
also be prepared on the substrate. Such multi-component bulk
catalysts are purchased from a commercial source and/or are
prepared by precipitation or co-precipitation protocols, and then
optionally treated--including mechanical pretreatment (grinding,
sieving, pressing). The bulk catalysts are placed on the substrate,
typically by slurry dispensing and drying, and then optionally
further doped with additional metal-containing components (e.g.
metal salt precursors) by impregnation and/or incipient wetness
techniques to form bulk catalyst precursors, with such techniques
being generally known to those of skill in the art. The bulk
catalyst precursors are treated by calcining and/or reducing to
form active bulk catalytic materials at discrete regions on the
wafer substrate.
The catalytic materials (e.g., supported or bulk) on the substrate
are tested for activity and selectivity for the WGS reaction using
a scanning mass spectrometer (SMS) comprising a scanning/sniffing
probe and a mass spectrometer. More details on the scanning mass
spectrometer instrument and screening procedure are set forth in
U.S. Pat. No. 6,248,540, in European Patent No. EP 1019947 and in
European Patent Application No. EP 1186892 and corresponding U.S.
application Ser. No. 09/652,489 filed Aug. 31, 2000 by Wang et al.,
the complete disclosure of each of which is incorporated herein in
its entirety. Generally, the reaction conditions (e.g. contact time
and/or space velocities, temperature, pressure, etc.) associated
with the scanning mass spectrometer catalyst screening reactor are
controlled such that partial conversions (i.e., non-equilibrium
conversions, e.g., ranging from about 10% to about 40% conversion)
are obtained in the scanning mass spectrometer, for discrimination
and ranking of catalyst activities for the various catalytic
materials being screened. Additionally, the reaction conditions and
catalyst loadings are established such that the results scale
appropriately with the reaction conditions and catalyst loadings of
larger scale laboratory research reactors for WGS reactions. A
limited set of tie-point experiments are performed to demonstrate
the scalability of results determined using the scanning mass
spectrometer to those using larger scale laboratory research
reactors for WGS reactions. See, for example, Example 12 of U.S.
Provisional Patent Application Ser. No. 60/434,705 entitled
"Platinum-Ruthenium Containing Catalyst Formulations for Hydrogen
Generation" filed by Hagemeyer et al. on Dec. 20, 2002.
Preparative and Testing Procedures
The catalysts and compositions of the present invention were
identified using high-throughput experimental technology, with the
catalysts being prepared and tested in library format, as described
generally above, and in more detail below. Specifically, such
techniques were used for identifying catalyst compositions that
were active and selective as WGS catalysts. As used in these
examples, a "catalyst library" refers to an associated collection
of candidate WGS catalysts arrayed on a wafer substrate, and having
at least two, and typically three or more common metal components
(including metals in the fully reduced state, or in a partially or
fully oxidized state, such as metal salts), but differing from each
other with respect to relative stoichiometry of the common metal
components.
Depending on the library design and the scope of the investigation
with respect to a particular library, multiple (i.e., two or more)
libraries were typically formed on each wafer substrate. A first
group of test wafers each comprised about 100 different catalyst
compositions formed on a three-inch wafer substrate, typically with
most catalysts being formed using at least three different metals.
A second group of test wafers each comprised about 225 different
catalyst compositions on a four-inch wafer substrate, again
typically with most catalysts being formed using at least three
different metals. Each test wafer itself typically comprised
multiple libraries. Each library typically comprised binary,
ternary or higher-order compositions--that is, for example, as
ternary compositions that comprised at least three components
(e.g., A, B, C) combined in various relative ratios to form
catalytic materials having a molar stoichiometry covering a range
of interest (e.g., typically ranging from about 20% to about 80% or
more (e.g to about 100% in some cases) of each component). For
supported catalysts, in addition to varying component stoichiometry
for the ternary compositions, relative total metal loadings were
also investigated.
Typical libraries formed on the first group of (three-inch) test
wafers included, for example, "five-point libraries" (e.g., twenty
libraries, each having five different associated catalyst
compositions), or "ten-point" libraries (e.g., ten libraries, each
having ten different associated catalyst compositions), or
"fifteen-point libraries" (e.g., six libraries, each having fifteen
different associated catalyst compositions) or "twenty-point
libraries" (e.g., five libraries, each having twenty different
associated catalyst compositions). Typical libraries formed on the
second group of (four-inch) test wafers included, for example,
"nine-point libraries" (e.g., twenty-five libraries, each having
nine different associated catalyst compositions), or "twenty-five
point" libraries (e.g., nine libraries, each having twenty-five
different associated catalyst compositions). Larger compositional
investigations, including "fifty-point libraries" (e.g., two or
more libraries on a test wafer, each having fifty associated
catalyst compositions), were also investigated. Typically, the
stoichiometric increments of candidate catalyst library members
ranged from about 1.5% (e.g. for a "fifty-five point ternary") to
about 15% (e.g., for a "five-point" ternary). See, generally, for
example, WO 00/17413 for a more detailed discussion of library
design and array organization. FIGS. 3A-3F of the instant
application shows library designs for libraries prepared on a
common test wafer, as graphically represented using Library
Studio.RTM. (Symyx Technologies, Inc., Santa Clara, Calif.), where
the libraries vary with respect to both stoichiometry and catalyst
loading. Libraries of catalytic materials that vary with respect to
relative stoichiometry and/or relative catalyst loading can also be
represented in a compositional table, such as is shown in the
several examples of this application.
Referring to FIG. 3A, for example, the test wafer includes nine
libraries, where each of the nine libraries comprise nine different
ternary compositions of the same three-component system. In the
nomenclature of the following examples, such a test wafer is said
to include nine, nine-point-ternary ("9PT") libraries. The library
depicted in the upper right hand corner of this test wafer includes
catalyst compositions comprising components A, B and X.sub.1 in 9
different stoichiometries. As another example, with reference to
FIG. 3B, a partial test wafer is depicted that includes a
fifteen-point-ternary ("15PT") library having catalyst compositions
of Pt, Pd and Cu in fifteen various stoichiometries. Generally, the
composition of each catalyst included within a library is
graphically represented by an association between the relative
amount (e.g., moles or weight) of individual components of the
composition and the relative area shown as corresponding to that
component. Hence, referring again to the fifteen different catalyst
compositions depicted on the partial test wafer represented in FIG.
3B, it can be seen that each composition includes Pt (red), Pd
(green) and Cu (blue), with the relative amount of Pt increasing
from column 1 to column 5 (but being the same as compared between
rows within a given column), with the relative amount of Pd
decreasing from row 1 to row 5 (but being the same as compared
between columns within a given row), and with the relative amount
of Cu decreasing from a maximum value at row 5, column 1 to a
minimum at, for example, row 1, column 1. FIG. 3C shows a test
wafer that includes a fifty-point-ternary ("50PT") library having
catalyst compositions of Pt, Pd and Cu in fifty various
stoichiometries. This test library could also include another
fifty-point ternary library (not shown), for example with three
different components of interest.
FIGS. 3D-3F are graphical representations of two fifty-point
ternary libraries ("bis 50PT libraries") at various stages of
preparation--including a Pt--Au--Ag/CeO.sub.2 library (shown as the
upper right ternary library of FIG. 3E) and a Pt--Au--Ce/ZrO.sub.2
library (shown as the lower left ternary library of FIG. 3E). Note
that the Pt--Au--Ag/CeO.sub.2 library also includes
binary-impregnated compositions--Pt--Au/CeO.sub.2 binary catalysts
(row2) and Pt--Ag/CeO.sub.2 (column 10). Likewise, the
Pt--Au--Ce/ZrO.sub.2 library includes binary-impregnated
compositions--Pt--Ce/ZrO.sub.2 (row 11) and Au--Ce/ZrO.sub.2
(column 1). Briefly, the bis 50PT libraries were prepared by
depositing CeO.sub.2 and ZrO.sub.2 supports onto respective
portions of the test wafer as represented graphically in FIG. 3D.
The supports were deposited onto the test wafer as a slurry in a
liquid media using a liquid handling robot, and the test wafer was
subsequently dried to form dried supports. Thereafter, salts of Pt,
Au and Ag were impregnated onto the regions of the test wafer
containing the CeO.sub.2 supports in the various relative
stoichiometries as represented in FIG. 3E (upper-right-hand
library). Likewise, salts of Pt, Au and Ce were impregnated onto
the regions of the test wafer containing the ZrO.sub.2 supports in
the various relative stoichiometries as represented in FIG. 3E
(lower-left-hand library). FIG. 3F is a graphical representation of
the composite library design, including the relative amount of
catalyst support.
Specific compositions of tested catalytic materials of the
invention are detailed in the following examples for selected
libraries.
Performance benchmarks and reference experiments (e.g., blanks)
were also provided on each quartz catalyst test wafer as a basis
for comparing the catalyst compositions of the libraries on the
test wafer. The benchmark catalytic material formulations included
a Pt/zirconia catalyst standard with about 3% Pt catalyst loading
(by weight, relative to total weight of catalyst and support). The
Pt/zirconia standard was typically synthesized by impregnating
3.mu.L of, for example, 1.0% or 2.5% by weight of Pt solution onto
zirconia supports on the wafer prior to calcination and reduction
pretreatment.
Typically wafers were calcined in air at a temperature ranging from
300.degree. C. to 500.degree. C. and/or reduced under a continuous
flow of 5% hydrogen at a temperature ranging from about 200.degree.
C. to about 500.degree. C. (e.g., 450.degree. C.). Specific
treatment protocols are described below with respect to each of the
libraries of the examples.
For testing using the scanning mass spectrometer, the catalyst
wafers were mounted on a wafer holder which provided movement in an
XY plane. The sniffing/scanning probe of the scanning mass
spectrometer moved in the Z direction (a direction normal to the XY
plane of movement for the wafer holder), and approached in close
proximity to the wafer to surround each independent catalyst
element, deliver the feed gas and transmit the product gas stream
from the catalyst surface to the quadrupole mass spectrometer. Each
element was heated locally from the backside using a CO.sub.2
laser, allowing for an accessible temperature range of about
200.degree. C. to about 600.degree. C. The mass spectrometer
monitored seven masses for hydrogen, methane, water, carbon
monoxide, argon, carbon dioxide and krypton: 2, 16, 18, 28, 40, 44
and 84, respectively.
Catalyst compositions were tested at various reaction temperatures,
typically including for example at about 200.degree. C.,
250.degree. C. and/or 300.degree. C. The feed gas typically
consisted of 51.6% H.sub.2, 7.4% Kr, 7.4% CO, 7.4% CO.sub.2 and
26.2% H.sub.2O. The H.sub.2, CO, CO.sub.2 and Kr internal standards
are premixed in a single gas cylinder and then combined with the
water feed. Treated water (18.1 mega-ohms-cm at 27.5.degree. C.)
produced by a Barnstead Nano Pure Ultra Water system was used,
without degassing.
Data Processing and Analysis
Data analysis was based on mass balance plots where CO conversion
was plotted versus CO.sub.2 production. The mass spectrometer
signals were uncalibrated for CO and CO.sub.2 but were based on
Kr-normalized mass spectrometer signals. The software package
SPOTFIRE.TM. (sold by SpotFire, Inc. of Somerville, Mass.) was used
for data visualization.
A representative plot of CO conversion versus CO.sub.2 production
for a WGS reaction is shown in FIG. 4A involving, for discussion
purposes, two ternary catalyst systems--a Pt--Au--Ag/CeO.sub.2
catalyst library and a Pt--Au--Ce/ZrO.sub.2 catalyst library--as
described above in connection with FIGS. 3D through 3F. The
catalyst compositions of these libraries were screened at four
temperatures: 250.degree. C., 300.degree. C., 350.degree. C. and
400.degree. C. With reference to the schematic diagram shown in
FIG. 4B, active and highly selective WGS catalysts (e.g., Line I of
FIG. 4B) will approach a line defined by the mass balance for the
water-gas-shift reaction (the "WGS diagonal") with minimal
deviation, even at relatively high conversions (i.e., at CO
conversions approaching the thermodynamic equilibrium conversion
(point "TE" on FIG. 4B). Highly active catalysts may begin to
deviate from the WGS diagonal due to cross-over to the competing
methanation reaction (point "M" on FIG. 4C). Catalyst compositions
that exhibit such deviation may still, however, be useful WGS
catalysts depending on the conversion level at which such deviation
occurs. For example, catalysts that first deviate from the WGS
diagonal at higher conversion levels (e.g., Line II of FIG. 4B) can
be employed as effective WGS catalysts by reducing the overall
conversion (e.g., by lowering catalyst loading or by increasing
space velocity) to the operational point near the WGS diagonal. In
contrast, catalysts that deviate from the WGS diagonal at low
conversion levels (e.g., Line III of FIG. 4B) will be relatively
less effective as WGS catalysts, since they are unselective for the
WGS reaction even at low conversions. Temperature affects the
thermodynamic maximum CO conversion, and can affect the point of
deviation from the mass-balance WGS diagonal as well as the overall
shape of the deviating trajectory, since lower temperatures will
generally reduce catalytic activity. For some compositions, lower
temperatures will result in a more selective catalyst, demonstrated
by a WGS trajectory that more closely approximates the WGS
mass-balance diagonal. (See FIG. 4C). Referring again to FIG. 4A,
it can be seen that the Pt--Au--Ag/CeO.sub.2 and the
Pt--Au--Ce/ZrO.sub.2 catalyst compositions are active and selective
WGS catalysts at each of the screened temperatures, and
particularly at lower temperatures.
Generally, the compositions on a given wafer substrate were tested
together in a common experimental run using the scanning mass
spectrometer and the results were considered together. In this
application, candidate catalyst compositions of a particular
library on the substrate (e.g., ternary or higher-order catalysts
comprising three or more metal components) were considered as
promising candidates for an active and selective commercial
catalyst for the WGS reaction based on a comparison to the
Pt/ZrO.sub.2 standard composition included on that wafer.
Specifically, libraries of catalytic materials were deemed to be
particularly preferred WGS catalysts if the results demonstrated
that a meaningful number of catalyst compositions in that library
compared favorably to the Pt/ZrO.sub.2 standard composition
included on the wafer substrate with respect to catalytic
performance. In this context, a meaningful number of compositions
was generally considered to be at least three of the tested
compositions of a given library. Also in this context, favorable
comparison means that the compositions had catalytic performance
that was as good as or better than the standard on that wafer,
considering factors such as conversion, selectivity and catalyst
loading. All catalyst compositions of a given library were in many
cases positively identified as active and selective WGS catalysts
even in situations where only some of the library members compared
favorably to the Pt/ZrO.sub.2 standard, and other compositions
within that library compared less than favorably to the
Pt/ZrO.sub.2 standard. In such situations, the basis for also
including members of the library that compared somewhat less
favorably to the standard is that these members in fact positively
catalyzed the WGS reaction (i.e., were effective as catalysts for
this reaction). Additionally, it is noted that such compositions
may be synthesized and/or tested under more optimally tuned
conditions (e.g., synthesis conditions, treatment conditions and/or
testing conditions (e.g., temperature)) than occurred during actual
testing in the library format, and significantly, that the optimal
conditions for the particular catalytic materials being tested may
differ from the optimal conditions for the Pt/ZrO.sub.2
standard--such that the actual test conditions may have been closer
to the optimal conditions for the standard than for some of the
particular members. Therefore, it was specifically contemplated
that optimization of synthesis, treatment and/or screening
conditions, within the generally defined ranges of the invention as
set forth herein, would result in even more active and selective
WGS catalysts than what was demonstrated in the experiments
supporting this invention. Hence, in view of the foregoing
discussion, the entire range of compositions defined by each of the
claimed compositions (e.g., each three-component catalytic
material, or each four-component catalytic material) was
demonstrated as being effective for catalyzing the WGS reaction.
Further optimization is considered, with various specific
advantages associated with various specific catalyst compositions,
depending on the desired or required commercial application of
interest. Such optimization can be achieved, for example, using
techniques and instruments such as those described in U.S. Pat. No.
6,149,882, or those described in WO 01/66245 and its corresponding
U.S. applications, U.S. Ser. No. 09/801,390, entitled "Parallel
Flow Process Optimization Reactor" filed Mar. 7, 2001 by Bergh et
al., and U.S. Ser. No. 09/801,389, entitled "Parallel Flow Reactor
Having Variable Feed Composition" filed Mar. 7, 2001 by Bergh et
al., each of which are incorporated herein by reference for all
purposes.
Additionally, based on the results of screening of initial
libraries, selective additional "focus" libraries were selectively
prepared and tested to confirm the results of the initial library
screening, and to further identify better performing compositions,
in some cases under the same and/or different conditions. The test
wafers for the focus libraries typically comprised about 225
different candidate catalyst compositions formed on a four-inch
wafer substrate, with one or more libraries (e.g. associated
ternary compositions A, B, C) formed on each test wafer. Again, the
metal-containing components of a given library were typically
combined in various relative ratios to form catalysts having
stoichiometry ranging from about 0% to about 100% of each
component, and for example, having stoichiometric increments of
about 10% or less, typically about 2% or less (e.g., for a
"fifty-six point ternary"). Focus libraries are more generally
discussed, for example, in WO 00/17413. Such focus libraries were
evaluated according to the protocols described above for the
initial libraries.
The raw residual gas analyzer ("rga") signal values generated by
the mass spectrometer for the individual gases are uncalibrated and
therefore different gases may not be directly compared. Methane
data (mass 16) was also collected as a control. The signals are
typically standardized by using the raw rga signal for krypton
(mass 84) to remove the effect of gas flow rate variations. Thus,
for each library element, the standardized signal is determined as,
for example, sH.sub.2O=raw H.sub.2O/raw Kr; sCO=raw CO/raw Kr;
sCO.sub.2=raw CO.sub.2/raw Kr and so forth.
Blank or inlet concentrations are determined from the average of
the standardized signals for all blank library elements, i.e.
library elements for which the composition contains at most only
support. For example, b.sub.avg H.sub.2O=average sH.sub.2O for all
blank elements in the library; b.sub.avg CO=average sCO for all
blank elements in the library; and so forth.
Conversion percentages are calculated using the blank averages to
estimate the input level (e.g., b.sub.avg CO) and the standardized
signal (e.g., sCO) as the output for each library element of
interest. Thus, for each library element,
CO.sub.conversion=100.times.(b.sub.avg CO-sCO)/b.sub.avg CO and
H.sub.2O.sub.conversion=100.times.(b.sub.avg
H.sub.2O-sH.sub.2O)/b.sub.avg H.sub.2O.
The carbon monoxide (CO) to carbon dioxide (CO.sub.2) selectivity
is estimated by dividing the amount of CO.sub.2 produced
(sCO.sub.2--b.sub.avg CO.sub.2) by the amount of CO consumed
(b.sub.avg CO-sCO). The CO.sub.2 and CO signals are not directly
comparable because the rga signals are uncalibrated. However, an
empirical conversion constant (0.6 CO.sub.2 units=1 CO unit) has
been derived, based on the behavior of highly selective standard
catalyst compositions. The selectivity of the highly selective
standard catalyst compositions approach 100% selectivity at low
conversion rates. Therefore, for each library element, estimated CO
to CO.sub.2 selectivity=100.times.0.6.times.(sCO.sub.2-b.sub.avg
CO.sub.2)/(b.sub.avg CO-sCO). Low CO consumption rates can produce
highly variable results, and thus the reproducibility of CO.sub.2
selectivity values is maintained by artificially limiting the
CO.sub.2 selectivity to a range of 0% to 140%.
The following examples are representative of the screening of
libraries that lead to identification of the particularly claimed
inventions herein
Example 1
A 4'' quartz wafer was precoated with commercial Ni bulk catalyst
(Engelhard, grade 0104P) by slurry dispensing the bulk Ni onto the
wafer. The slurry was composed of 1 g of the bulk Ni dissolved in 4
mL of a methyl oxide ("MEO")/ethylene glycol ("EG")/H.sub.2O
(4:3:3).
The bulk Ni-precoated wafer was dried and then six internal
standards were dispensed into six first row/last column wells (4
.mu.L of zirconia slurry+3 .mu.L of a 2.5%
Pt(NH.sub.3).sub.2(NO.sub.2).sub.2 solution). The wafer was dried
and then impregnated with gradients of 15 metals by Cavro
dispensing from In nitrate (0.5M), Mn nitrate (0.5M), Sn oxalate
(0.5M), Pb nitrate (0.5M), Te acid (0.5M), sulfuric acid (0.1M), Cd
nitrate (0.5M), Ni sulfate (0.1M), ammonium-antimony-oxalate
(0.3M), Sn sulfate (0.1M), Ge oxalate (0.5M), In sulfate (0.1M), Bi
nitrate (0.5M), Cd sulfate (0.1M) and Zn nitrate (0.5M) stock
solution vials to a microtiter plate. A replica transfer of the
microtiter plate pattern to the wafer followed (3 .mu.L dispense
volume per well). The wafer was dried and then reduced in 5%
H.sub.2/N.sub.2 at 380.degree. C. for 2 hours. A commercial
catalyst was slurried into 5 positions of the first row and last
column as an external standard (3 .mu.L per well). See FIGS. 1A and
1B.
The reduced library was then screened by scanning mass spectrometry
("SMS") for WGS activity with a H.sub.2/CO/CO.sub.2/H.sub.2O mixed
feed at 330.degree. C. and 360.degree. C. See FIGS. 1C and 1D.
This set of experiments demonstrated active and selective WGS
catalyst formulations of various modified bulk Ni formulations on
the wafer.
Example 2
Scale-up catalyst samples were prepared by using incipient wetness
impregnation of 0.75. grams of ZrO.sub.2 support (Norton, 80-120
mesh) which had been weighed into a 10-dram vial. Aqueous metal
precursor salt solutions were then added in the order: Ni, then one
or more of Cd, In, and Sn. The precursor salt solutions were
nickel(II) nitrate hexahydrate (1.0 M), cadmium nitrate in
NH.sub.4OH 20% (w/w) (0.25 M), indium (III) nitrate (1.0 M), and
tin (II) tartrate hydrate in (CH.sub.3).sub.4NOH 25% (w/w) (0.25
M). All starting reagents were nominally research grade from
Aldrich, Strem, or Alfa. Following each metal addition, the
catalysts were dried at 80.degree. C. overnight and then calcined
in air as follows:
TABLE-US-00001 After Ni addition 450.degree. C. for 3 hours After
Cd, In, or Sn addition 450.degree. C. for 3 hours
Catalyst Testing Conditions
Catalysts were tested in a fixed bed reactor. Approximately 0.15 g
of catalyst was weighed and mixed with an equivalent mass of SiC.
The mixture was loaded into a reactor and heated to reaction
temperature. Reaction gases were delivered via mass flow
controllers (Brooks) with water introduced with a metering pump
(Quizix). The composition of the reaction mixture was as follows:
H.sub.2 50%, CO 10%, CO.sub.2 10%, and H.sub.2O 30%. The reactant
mixture was passed through a pre-heater before contacting the
catalyst bed. Following reaction, the product gases were analyzed
using a micro gas chromatograph (Varian Instruments, or Shimadzu).
Compositional data on the performance diagram (FIG. 2) is on a dry
basis with water removed.
Testing Results
FIG. 2 shows the CO composition in the product stream following the
scale-up testing at a gas hour space velocity of 50,000
h.sup.-1.
TABLE-US-00002 TABLE 1 Catalyst Compositions (mass ratio) Row Col
Ni Cd In Sn A 1 0.96 0.04 0 0 B 1 0.953 0.032 0.015 0 B 2 0.953
0.032 0 0.015 C 1 0.946 0.024 0.03 0 C 2 0.946 0.024 0.015 0.015 C
3 0.946 0.024 0 0.03 D 1 0.939 0.016 0.045 0 D 2 0.939 0.016 0.03
0.015 D 3 0.939 0.016 0.015 0.03 D 4 0.939 0.016 0 0.045 E 1 0.932
0.008 0.06 0 E 2 0.932 0.008 0.045 0.015 E 3 0.932 0.008 0.03 0.03
E 4 0.932 0.008 0.015 0.045 E 5 0.932 0.008 0 0.06 F 1 0.925 0
0.075 0 F 2 0.925 0 0.06 0.015 F 3 0.925 0 0.045 0.03 F 4 0.925 0
0.03 0.045 F 5 0.925 0 0.015 0.06 F 6 0.925 0 0 0.075
* * * * *
References